196 SENSE OF HEARING. 



foramen ovale : our knowledge, however, is restricted to the fact, that 

 its tension can be varied by the chain of ossicles, without our being 

 able to specify the circumstances under which this takes place. M. 

 Adelon asserts, that the membrane may be torn, and yet the sense of 

 hearing not be destroyed. This seems scarcely possible, as the liquor 

 of Cotunnius must necessarily escape, and so much morbid action be 

 induced as to render audition impracticable. 



The membrane of the foramen rotundum, which forms the medium 

 of communication between the cavity of the tympanum and the cochlea, 

 has no chain of bones to modify its tension. The vibrations into which 

 it is thrown, as well as those of the vestibular membrane, are imparted, 

 as we have seen, to the liquor of Cotunnius, which is present in every 

 ear, and appears essential to audition. 



Of the precise use of the vestibule, semicircular canals, and cochlea, 

 we have very limited notions. The beauty and complexity of their 

 arrangement has given rise to various conjectures. M. Le Cat 1 con- 

 sidered the lamina spiralis to consist of numerous minute cords, stretched 

 along it, and capable of responding to every tone. M. Magendie 2 

 affirms, that no one admits the hypothesis regarding the use of this 

 osseo-membranous septum ; but he is in error. Sir C. Bell 3 asserts, 

 that the cochlea is the most important part of the organ of hearing ; 

 or rather, that it is "the refined and higher part of the apparatus;" 

 and he considers the lamina spiralis as the only part adapted to the 

 curious and admirable powers of the human ear for the enjoyment of 

 melody and harmony. The subject of the musical ear will engage us 

 presently. It may be sufficient to remark, that there is no ratio in 

 animals, between their delicacy of hearing arid the degree of compli- 

 cation of the cochlea. The cochlea of the Guinea pig is more convoluted 

 than that of man ; yet we can hardly conceive it to have a better ap- 

 preciation of musical tones ; whilst in birds, whose hearing is delicate, 

 the organ is, as we have remarked, simple, and has no spiral arrange- 

 ment. 



Again; the semicircular canals have been compared to organ pipes, 

 adapted for producing numerous tones ; and Dr. Young 4 supposes them 

 to be " very capable of assisting in the estimation of the acuteness or 

 pitch of a sound, by receiving its impression at their opposite ends ; 

 and occasioning a recurrence of similar effects at different points of 

 their length according to the different character of the sound ; while 

 the greater or less pressure of the stapes must serve to moderate the 

 tension of the fluid within the vestibule, which serves to convey the 

 impression." " The cochlea," he adds, " seems to be pretty evidently 

 a micrometer of sound." Another view to be remarked upon here- 

 after is, that their peculiar function is the reception of the impressions 

 by which we distinguish the direction of sounds. All these are mere 

 hypotheses ; ingenious, it is true, but still hypotheses ; and, in candour, 

 it must be admitted, that we have no positive knowledge of the precise 

 functions of either vestibule, cochlea, or semicircular canals. Our 



1 Traite des Sens, Paris, 1767, or English translation, London, 1750. 



3 Precis, &c., i. 121. 3 Op. citat., ii. 273. Med. Literature, p. 98, London, 1813. 



